| Abstract |
- Metropolitan solid wastes and sewage sludges present a serious
disposal problem for many communities. To assess the feasibility of
disposal or utilization of these waste products on soils, a study was
initiated to evaluate plant growth and soil elemental interactions on a
loamy fine sand treated with metropolitan waste. Shredded municipal
refuse and sewage materials were added to Sagehill loamy fine sand in
both irrigated field plots and laboratory lysimeters at rates of 0, 100,
200, and 400 ton/acre and 0, 5500, 11,000, and 22,000 gal/acre,
respectively. Ammonium sulfate fertilizer was added in 1972 to the
fescue and alfalfa plots at rates of 250, 500, 1000, and 2000 lb of
N/acre/year and 80, 200, 400, and 600 lb of N/acre/year, respectively.
Fawn fescue and Sernac alfalfa yields were measured and soil
and plant samples collected for chemical analysis. Shredded metropolitan waste and sewage sludge at rates
comparable to the field study were added to plexiglass columns,
ten in x three ft, packed with Sagehill loamy fine sand to simulate the
natural soil profile. Nitrogen fertilizer, 240 lb N/acre/2 week
interval, was added and the columns were either continuously,
1.4 in/2 day, or intermittently, 1.4 in/2 hr every 2 days, leached.
Approximately the same volume of water was applied to all
columns. The columns were leached for six months, allowed to dry
for six months, and then leached an additional 28 days to simulate a
second year of leaching. Percolation water samples were collected
for chemical analysis.
The concentration of Na, K, Ca, Mg, Fe, Mn, Cu, Zn, B, P,
and organic-N in the Sagehill loamy sand on the field plots and in the
laboratory lysimeters increased with waste additions. The concentration
of NO₃-N and NH₄-N increased mainly as a result of N fertilizer
additions.
The pH of the surface soil decreased to approximately 5.0 with
the addition of ammonium sulfate; however, the pH of the leachate
from the soil columns remained above 7.0 because of the carbonate
accumulation in the lower portion of the soil profile. Sodium in comparison
to Mg, Ca, and K leached through the soil columns most
rapidly; however much of the added Na was not leached. Iron movement
in the soil profile of the leaching columns related directly to a decrease in pH and the development of reducing conditions. The
concentration of extractable Mn in the soil increased with the decrease
in the pH of the surface soil associated with the ammonium sulfate
fertilizer application. The concentration of extractable Cu, Zn, and
P in the soil to the incorporation depth of the refuse was very high
compared to the check soil as a result of Cu, Zn, and P additions in
the waste and a decrease in pH. Very little movement of Cu, Zn, or
P occurred below the incorporation depth of the refuse.
The NO₃-N moved readily through the profile of the waste
treated plots. Comparatively little NH₄-N moved through the profile
of the field plots. The NH₄-N and NO₃-N did not appear in the leachate
from the waste treated columns until after a delay of 40-90 days.
This delay was due to the immobilization of the added nitrogen by
increased microbial activity. In the second simulated year of leaching
the NO₃ -N concentration of the leachate from the waste treated
columns increased from a range of 0.28 to 49 ppm at the end of year
one to 18 to 400 ppm. The NO₃ -N concentration subsequently decreased
rapidly to 0.42 to 43 ppm with additional water application.
Data from the field plots most closely paralleled the data from
the intermittently leached columns while the continuously leached columns
represented a more extreme environment particularly with
regard to the reducing conditions that developed in them. Unless
strong reducing conditions occurred in the profile, NO₃-N was the only ion studied which posed an apparent threat to ground water quality.
Land application of municipal refuse at levels less than
400 ton/acre is a suitable method of disposal. The optimum rate
appeared to be 100 ton/acre. At this rate the refuse was easily
incorporated into the soil, plant elemental uptake problems were
minimal, and unfavorable chemical changes such as the development
of reducing conditions in the 400 ton/acre refuse treated plots did not
generally occur.
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